1. Field of the Invention
This invention relates to an antenna configuration in a primarily rectangular or trapezoidal aperture of an electrically conductive vehicle chassis in the meter wavelength range, for example for UHF reception.
2. The Prior Art
The invention is based on an antenna system as described, for example, in German Patent 195 35 250 A1 in FIG. 4a of the roof segment for a small vehicle. The antennas described therein for frequencies up to the meter wave length region are preferably designed as thin conductive wires. Due to the limited available space in vehicle construction, primary consideration for locating the above-described segments is given to roof segments or segments in the conductive trunk cover. The aperture length L is constrained by the width of the vehicle. Its aperture width B is also constrained by other technical structural requirements, e.g. sliding roof, roll-over security, etc. This results, in particular, in the range of meter wavelengths, to a choice of aperture length L often less than one-half of the operating wavelength, and an aperture width B less than 1/10 of the operating wavelength. In this case, the objective of a low-loss adaptation with the largest achievable bandwidth cannot be realized with the proposed antennas in FIG. 4a of German Patent 195 35 250 A1. Even for larger passenger cars, an aperture length L of greater than 90 cm is hardly available. This means that in the UHF range, for a center FM frequency of 97 MHz, an aperture length L of L/λ=0.3 with a relative bandwidth in the UHF region of (fmax−fmin/fm)=0.211. For the FM-Band in Japan with its center frequency of=83 MHz, this means that, for the wavelength of this frequency, a relative aperture length L of L/λ=0.25 with a relative bandwidth in the UHF region of fmax−fmin/fm=0.17. For the proposed antennas to conform to the impedances customary in antenna technology, they will have the disadvantage of a narrow bandwidth. Alternatively, the matching bandwidth can only be achieved with losses. For example, the operating frequency bandwidths in the above-referenced frequency bands, given the aperture lengths L of L/λ=0.3, and L/λ=0.25, respectively, cannot be realized with sufficiently low losses, i.e. the efficiency-bandwidth product is too small.